The purpose of this study is to investigate the efficacy and safety of the lifileucel regimen in participants with previously treated endometrial cancer.

The study will enroll participants with advanced endometrial cancer who previously received treatment with platinum-based chemotherapy and an anti-programmed cell death protein-1 (PD-1)/programmed death ligand 1 (PD-L1) agent in a recurrent or advanced setting, either sequentially or in combination.

Inclusion Criteria:

1. Participants must have a histologically confirmed diagnosis of endometrial carcinoma. All histologies, including carcinosarcoma, will be allowed. Uterine sarcoma will not be allowed.

2. Participants who have received the following previous therapies:

   • At least 1 but no more than 4 lines of prior systemic therapy with no more than 2 lines of chemotherapy in any setting (ie, neoadjuvant or adjuvant setting as well as for recurrent, metastatic, or primary unresectable disease. .
   • Participants have received platinum-based chemotherapy and anti-PD-1/PD-L1 therapy.
   • Participants who declined platinum-based chemotherapy regimen and/or an anti-PD-1/PD-L1 therapy or were deemed ineligible for such therapies by the investigator may be considered after discussion with the medical monitor.
   • Systemic therapy counting towards lines of therapy includes chemotherapy, targeted therapy, immunotherapy, and antibody drug conjugates, given alone or in combination. Hormonal therapy does not count as a line of therapy.
   • Participants must have either (i) documented radiographic disease progression during or after the last line of therapy or (ii) discontinued their last line of therapy because of treatment intolerance or toxicity or (iii) with medical monitor discussion, participant/physician decision in the context of stable disease with evidence of tumor growth.

3. Participants who have an Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1 and estimated life expectancy of >6 months.

4. Participants having at least one resectable lesion and at least one measurable lesion, following resection of the lesion for TIL generation.

5. Participants who have adequate organ function, including adequate cardiopulmonary function.

6. Participants of childbearing potential must be willing to practice an approved method of highly effective birth control during treatment and up to 12 months after the last dose of study intervention.

7. Participants who are >70 years of age may be allowed to enroll after the investigator discusses with the medical monitor.

Exclusion Criteria:

1. Participants who have symptomatic untreated brain metastases.
2. Participants who have had a history of allogeneic organ transplant or any form of cell therapy involving prior conditioning chemotherapy within the past 20 years.
3. Participants who require systemic steroid therapy > 10 mg/day prednisone or another steroid equivalent dose.
4. Participants who have any form of primary immunodeficiency.
5. Participants who have another primary malignancy within the previous 3 years.
6. Participants who have received or will receive a live or attenuated vaccination within 28 days prior to the start of the NMALD.